1. Field of the Invention
This invention relates to a disconnect switch for use with a metal-encapsulated high-voltage switching installation wherein the switch comprises a movable switching pin and a mating contact axially associated therewith.
2. Description of the Prior Art
In disconnect switches of the above type, the movable switching pin is actuated by a motor drive, which requires between 5 to 10 seconds to close the switch. The actual closing time depends on the size of the gap between the switching pin and the mating contact which, in turn, is a function of the nominal voltage.
If a disconnect switch of this type is closed, a preliminary breakdown with a subsequent arc of low current always occurs, if the disconnect switch is operated under voltage. In such case, the burning time of the preliminary arc may be several seconds. For disconnect switches which are suitable for voltages of up to 245 kV, the preliminary breakdown distance is so small, especially if sulfur hexafluoride is used as the quenching and insulating medium of the metal-encapsulated installation, that the arc is not expected to wander off while it burns.
On the other hand, in disconnect switches for voltages higher than 245 kV, the preliminary breakdown distance is larger so that there exists a definite danger that the preliminary arc may wander from its point of origin to the grounded encapsulation of the installation.
It is, therefore, an object of the present invention to provide a disconnect switch suitable for operation at voltages above 245 kV which does not suffer from the above disadvantage.